LA_SBEV and LA_SBEVD compute all eigenvalues and, optionally,
all eigenvectors of a real symmetric matrix in band form.
LA_HBEV and LA_HBEVD compute all eigenvalues and, optionally,
all eigenvectors of a complex Hermitian matrix in band form.
LA_SBEVD and LA_HBEVD use a divide and conquer algorithm.
They are much faster than LA_SBEV and LA_HBEV for large matrices
but use more workspace.